As electronic systems become more compact, and the tolerances between individual components are required to be maintained to precise specifications, the effects of thermal expansion based on heat generated by, or dissipated through, individual component may modify such clearances in a manner that requires some compensation. Such compensation may be provided, for example, by a programmable electrical power biasing circuit.
Programmable electrical power biasing circuits are used in many and widely varied applications. For example, such circuits may be used in hard disk driver control and operating systems. In such systems, separation distances between a sensing head and a recording medium must often be maintained to the types of strict tolerances discussed briefly above. Often, one or more resistive elements are used as part of the sensing head. These resistive elements are subject to amounts of electrical power being dissipated through them. A resulting change in temperature results in a characteristic thermal expansion which, in turn, affects the separation distance between the sensing head and the recording medium. Through active control of power dissipated through the one or more resistive elements, the thermal expansion may be predictably modified, and, the separation distance between the sensing head and the recording medium may be predictably set, controlled or varied. In other words, by controlling the electrical power dissipation through the one or more resistive elements of the sensing head precise control of the separation distance may be controlled.
The resistive element is often biased such that it dissipates a predetermined amount of electrical power precisely through it resulting in repeatable heat generation and associated thermal expansion. In order to precisely set an electrical power dissipation, an electrical power calibration routine is generally performed during, in conjunction with, or at some point subsequent to, a power-up cycle of the system within which the resistive element is located. Such calibration attempts to nullify any potential deviation in thermal expansion by adjusting the power to be dissipated through the resistive element according to an adjustment factor. The adjustment factor is arrived at through the calibration routine. While generally only one calibration routine is required, more than one calibration routine may be undertaken sequentially or during predetermined, scheduled, or random breaks at intervals in an operating cycle of the system. When only one calibration routine is undertaken, or a series of calibration routines are initiated, just after the power-up cycle, an adjustment factor is determined and applied to the system such that subsequently during the operating cycle of the system a predetermined amount of electrical power to be dissipated through the resistive element is precisely controlled in order to limit deviations in heat generation and the accompanying thermal expansion through the system.